The present invention relates primarily to the retention of mining, trenching and construction tools or bits which are comprised of a hardened steel body with a hard tip and which are retained by a hardened steel retainer sleeve. These tools are mounted to drums, chains and wheels in various orientations and quantity. The bit is then engaged in soft rock formations ranging from asphalt to sandstone. The hard tip fixed to the end of the tool directly engages the material being mined or cut.
Typically the retainer sleeve retains the tool axially while allowing free rotation of the tool during service, as disclosed for example in Hedlund et al., U.S. Pat. No. 4,921,310.
For example, as shown in accompanying FIG. 1, a retainer sleeve 10 is disclosed for retaining a rotary tool 14 in a bore 16 of a holder 18. The sleeve includes tongues 20 that are deformed radially inwardly from a cylindrical portion 22 of the sleeve to engage in an annular groove 24 of the tool. The cylindrical portion 22 continues rearwardly past the tongues 20 and is situated between the outer periphery of a rear flange 26 of the tool and a wall 28 of the bore in order to prevent the flange from contacting the bore wall. The inner diameter of the retainer sleeve is larger than the outer diameter of the tool, to ensure that the tool can freely rotate relative to the stationary retainer sleeve.
It has been discovered that during cutting operations, especially the cutting of gummy materials, such as hot asphalt, fines such as dirt and cuttings can become trapped and packed within the annular groove 24, thereby filling the gap and opposing free rotation of the tool. As a result, a wear flat will develop on the hard tip of the tool progressing down onto the steel body. After developing a wear flat, the tool rotation generally stops, whereby the remaining useful tool life is lost.
Another prior art arrangement described in the Hedlund et al. patent is depicted in accompanying FIG. 2. In that arrangement, the entire rear edge portion of a cylindrical retainer sleeve 32 is bent inwardly to form a flange 30 which is inclined in an axially rearward, radially inward direction and is received in an annular groove 34 of a tool 36. It will be appreciated that an inward bending of the entire rear portion of the sleeve causes the material of the sleeve to bulge radially outwardly at the annular junction between the cylindrical portion 38 of the sleeve and the bent portion 30. That protrusion becomes squeezed between the bore wall and the tool when the tool/sleeve assembly is forced into the bore, thereby applying considerable friction against the tool tending to resist free rotation thereof. Also, since the flange extends continuously in the circumferential direction there is less ability for fines trapped between the flange 30 and a front surface of the groove 34 to escape rearwardly.
One additional prior art arrangement is disclosed in German Patent Document 3712 427 and depicted in the accompanying FIG. 3. In that arrangement, a rear portion of a retainer sleeve 42 is deformed to form tongues 40 that are bent radially inwardly into an annular groove 44 of a tool 46. The deformation step for producing each tongue is performed after a short sleeve-weakening slit has been formed in a cylindrical portion of the sleeve, the slit extending in the circumferential direction. The slits associated with respective tongues are spaced apart from one another in the circumferential direction. Each tongue thus forms a shoulder 48 extending perpendicular to the center axis of the sleeve. That shoulder extends parallel to an opposing front surface 50 of the annular groove 44 to form a gap therebetween from which fines have difficulty exiting, and can result in the above-mentioned opposition to tool rotation.
It is, therefore, an object of the present invention to provide a tool/sleeve assembly which facilitates free rotation of a tool and minimizes a tendency for fines to become packed in a manner preventing such free rotation.
The present invention relates to a cutting assembly which comprises a holder, a cutting tool body, and a retainer sleeve. The holder includes a bore having a cylindrical bore wall of a first diameter. The cutting tool body defines a longitudinal center axis and includes a front head, a shank, a rear flange, and an annular groove. The front head has a cutting tip, and the shank extends rearwardly from the front head and into the bore. The shank includes an outer cylindrical surface of a second diameter smaller than the first diameter. The rear flange is disposed at a rear end of the shank and is situated within the bore. The rear flange includes an outer cylindrical surface of a third diameter no greater than the second diameter. An annular radial gap is formed between the bore wall and the outer cylindrical surface of the rear flange. The annular groove is formed in the outer cylindrical surface of the shank immediately in front of the rear flange. The groove includes a forwardly facing stop surface. The retainer sleeve retains the tool body axially within the bore while permitting the tool body to rotate freely about the axis. The retainer sleeve includes a cylindrical portion which is slit longitudinally in half and situated radially between the outer surface of the shank and the bore wall. The cylindrical portion is elastically compressed radially by engagement with the bore wall to tightly engage the bore wall. An inner surface of the radially inwardly compressed cylindrical portion has a fourth diameter greater than the second diameter. The retainer sleeve includes circumferentially spaced tongues bent inwardly from the cylindrical portion and extending into the groove to axially retain the tool body in the bore, while permitting the tool body to rotate freely about the axis. Each tongue is inclined in a direction axially rearwardly and radially inwardly from the cylindrical portion, to form an oblique angle with the axis. A longitudinal length of the retainer sleeve is dimensioned such that when the tool is rearwardly pressured during a cutting operation, the tongues are essentially out of continuous contact with the surfaces of the groove, and a rear edge of the cylindrical portion and rear edges of the tongues are spaced forwardly from the forwardly facing stop surface.
The invention also pertains to a cutter tool assembly comprising the body and the retainer sleeve.